The present invention relates to a semiconductor device, or more in particular to a MIS (metal insulator semiconductor) transistor which makes possible the reduction in size of a complementary-type circuit or the like having double functions of P-type and N-type channel MIS transistors such as CMOS.
With the advance in size reduction of MIS transistor, there has been a corresponding increasing demand for consideration of the short-channel effect or the hot carrier effect. The short-channel effect is defined as a phenomenon especially related to a P-type channel MIS transistor in which the increased proximity between the source and drain with size reduction of the device causes the potential of the channel to be affected by the drain voltage reducing the threshold voltage or punch-through voltage. The hot carrier effect, on the other hand, is a phenomenon specially related to an N-type channel MIS transistor in which electrons flowing in the channel are implanted toward the gate by scattering, and electrons and holes generated by a weak breakdown are also implanted. This last-mentioned phenomenon is likely to occur more, the higher the drain voltage, and the maximum voltage applicable for long time to a submicron device is determined by the hot-carrier breakdown voltage.
In the prior art, a lightly doped drain (hereinafter referred to as "LDD") as shown in FIG. 6 has been used for the hot carrier effect. In FIG. 6, a gate electrode 6 is formed in the surface of a P-type well region 2b formed in a semiconductor substrate 1 through a gate insulating film 5, and a field insulating film 7 in an element isolation region. After that, ions are implanted with the gate electrode 6 and the field insulating film 7 masked thereby to form an N.sup.- -type diffusion layer 8 of low impurity concentration. Spacers 9 are provided on both sides (side walls) of the gate electrode 6, and ions are implanted with the gate electrode 6, spacer 9 and the field insulating film 7 masked thereby to form an N.sup.+ -type diffusion layer 10 of high impurity concentration and with the bottom thereof diffused deeper than the bottom of the N.sup.- -type diffusion layer 8.